Method of marking tungsten carbide



Dec. 27, 1949 D. c. FONDA METHOD OF MARKING TUNGSTEN CARBIDE Filed 001:. 25, 1945 INVENTOR Q Q QK W ATTORNEY Patented Dec. 27, 1949 UNITED STATES PATENT OFFICE METHOD OF MARKING TUNGSTENCARBIDE Douglass C; Fonda, stamrormioonn.

Application-OctoberZS, 1945; serial No.- 624,432

. 3 Claims. (Cl. 204143.),

This invention relates to the marking. of legends, such as size designations, on articles made of tungsten carbide.

Conventional methods of marking steel parts cannot be used effectively on tungsten carbide which resists the action of acids that are used for etching. Tungsten carbide can be marked with diamonds, but the process is costly, so cost.- ly in fact that it has been the practice to sell tungsten carbide parts without size designations.

It is an object of this invention to provide an improved method for marking tungsten carbide parts. The invention is convenient to use, marks the parts quickly and is economical. Al.- though it will be described in connection with the marking of gage blocks, the invention is suitable for marking tungsten carbide parts generally.

The process of this invention utilizes an electric current passed through a liquid electrolyte, preferably an acid, that contacts with the surface to be etched only along the lines of the marks to be made. I

Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.

In the drawings, forming a part here0f,,in which like reference characters indicate corresponding parts in all the views,

Figure 1 is a diagrammatic sectional. view showing a tungsten carbide element coated with a resist, and illustrating the way in which markings are made through the resist with a scriber.

Figure 2 is a large-scale side view, mostly in section, showing the process of marking atungsten carbide gage block in accordance withthis invention.

Figure 3 is a front elevation on a reduced scale, showing the gage block of Figure 2 after it has been marked.

In carrying out the process of this invention for marking tungsten carbide gage blocks, a coating of resist I l is first applied to the surface that is to be marked. Although no electrolyte comes in contact with the sides of the blockwhen the process is carried out in the intended manner, the coating of resist is preferably applied to the sides of the block also as a protection since some electrolyte may accidentally run down the sides. The resist is a non-conductor of electricity and usually a finely ground powder carried by a vehicle, for example carbon tetrachloride. Commercial products are available on the market, one such resist is Holsapples Ground.

In order to etch a fine line, such as is used for gage block marking, it is necessary that the resist be made of finely ground material so that a thin line can be cut through the resist by means of a scriber or stylus 13. The scriber I3 is preferably moved by a pantagraph which operates against letter or numeral guides for obtainingperfect letters or figures;

The line out in the resist by the scriber is designated in Figure 1: by the reference character I4.

Afterthenecessaryinscriptions have been cut throughv theresist: coating II, a drop of liquid ill is placed.- on the: resist over the lines made by the scriber. The block l0, which is to be marked at an" upper end-with a size designation, and below-its mid region with the manufacturers nameand aserial number, is shown in Figure 2 withtwo globules of liquid I! placed in position to cover the-areasof the markings.

It is unnecessaryto-spread theliquidll over areas of the block that are not to be marked, but no' harmis clone in having such areas covered by the liquid l'l since the resist prevents the liquidfrom coming'in contact with the metal of. areas not exposedby the scriber. When etching gageblocks one'drop of liquid is used for each line of. marking, or a large drop for two lines-located close together, and it is advantageous to apply the liquid as drops or globules so thattheliquid does not flow beyond the edges of the resist and'down over the side surfaces of the block.

Theliquid ll, which "serves as an electrolyte during its etching process is preferably an acid, butother liquids can be used, even water.

In order to etch'the block a pointed electrode 20 is brought intocontact with one of the drops of electrolyte I1 and a high intensity current at low voltage is passed from'the electrode 20 through the electrolyte ll to the block Ill. The un'coated bottom surface of the block It rests on ametalsupport 2| that is connected in the circuit with the electrode 20. The power is ordinarily supplied from a transformer 22 in which the voltage can be stepped down from thatiof aprimary supply source 24.

The electrode 20. shown in Figure 2 has a pointed'end, but it is not essential that the end of." the electrode be-pointeol. It is a feature of the invention; however, that the electrode is brought into contact with the drop or globule ll 'of the electrolyte'but not with the coating of resist H. The disadvantage of touching the electr'ode'tothe coatin il is that the coating is likely'to be-broken by the mechanical contact, and the distribution of current through the regions cut in the resist is more uniform if the "electrode ll'is merely brought into contact with the upper-portionof the globule II.

It is not essential that the electrode touch the globule II in the middle, and in the operation 'i IIustrated inFigureQ the electrode 23 is shown in contact with one side'of the globule ll. With a dilute acid globule and a current of 25 amperes, it is necessary to maintain the electrode as in contact with the electrolyte I! for only one or two seconds in order to mark the gage block.

Using Water as the electrolyte increases the time to a period of from six to ten seconds. The secondary voltage of the transformer 22 for these illustrations is 12 volts. These values are given as merely illustrative. Longer periods of current fiow result in deeper etching of the tungsten carbide surface. For marking gage blocks, thin lines without deep etching tend to keep the block from warping, they are considered more attractive in appearance, and they have the practical advantage that less subsequent lapping of the block is required to remove any upset of the metal caused by the etching operation.

Experience has shown that this process produces legends around which there is no noticeable burr or upset unless the surface is subjected to the exacting scrutiny of the optical instruments used in testing the flatness of gage blocks.

With such instruments a slight upset is found along the edges of the etched legends, and in gage block manufacture the etching is therefore done after the rough lapping and before the final finish lapping of the surfaces of the blocks.

The electrode 20 is applied to the globules I! by hand, and it is provided with a coating of insulation 25 that provides a convenient handle by which the electrode can be gripped by the operator using it. The electrode 20 is preferably made of brass and the handle 26 of rubber, wood or other insulating material which is light and easily held.

When the current has flowed through the globule I! long enough to etch the tungsten carbide, the electrode is removed and the globule I1 is blotted off the surface. The block is then washed in naphtha or any other suitable liquid for removing the coating of resist H. gure 3 shows the block after the resist has been removed and shows the regions etched in the block by the passage of the heavy electric current.

The preferred embodiment of the invention has been illustrated and described, but changes and modifications can be made and the current applied in ways other than those illustrated without departing from the invention as defined in the claims.

I claim as my invention:

1. The method of marking tungsten carbide gage blocks, which method comprises coating the gage block with a resist after the block has been rough lapped and before the final lapping of the block to size, marking a size designation or other symbol through the resist over a relatively small area of the block by means of a sharp pointed scriber, placing liquid electrolyte over the marks cut through the resist by said scriber, the liquid electrolyte being limited to a globule that has a generally convex top surface maintained at a substantial distance above the surface of the resist by the surface tension of the liquid electrolyte, bringing the point of a metal electrode into contact with the electrolyte over an area substantially less than the area of contact of the globule with the block and without touching the resist or the gage block, passing an electric current from the electrode through the electrolyte to the surface of the gage block exposed through the markings out in the resist, continuing the flow of current until the block is marked to the desired depth, and thereafter lapping the block to final gaging dimensions and flatness.

2. The method of marking size designations and other legends on a relatively small area of the gaging surfaces of tungsten carbide gage blocks, which method comprises coating a gaging surface of the block with a resist after the block has been rough lapped and before the final 1apping of the gaging surfaces, cutting fine outlines of the numerals or other legends to be etched in the block by means of a sharp pointed scriber that pierces the resist and bears against the metal of the face to be etched, placin a drop of electrolyte over each line of legends cut by the scriber to form globules of liquid on the resist, each drop of liquid electrolyte being limited to a globule that has a generally convex top surface maintained at a substantial distance above the surface of the resist by the surface tension of the liquid electrolyte, which globules terminate short of the edges of the block, bringing a point of a metal electrode into contact with each drop of liquid successively over an area substantially less than the area of contact of the globule with the block, holding the electrode out of contact with the resist and the metal of the block, passing an electric current of approximately 25 amperes from the electrode through the electrolyte to the metal exposed through the lines cut through the resist for a period of approximately two seconds, removing the electrode, blottin the globules of liquid from the block, washing the resist from the block and thereafter lapping the block to remove the metal upset by the etching process.

3. The method of marking tungsten carbide parts, which method comprises coating the part with resist, marking a size designation or other symbol through the resist, over a relatively small area of the part, by means of a sharp-pointed scriber, placing a liquid electrolyte over the marks cut through the resist by said scriber, the liquid electrolyte bein limited to a globule that has a. generally convex top surface maintained at a substantial distance above the surface of the resist by the surface tension of the liquid electrolyte, bringing the point of a metal electrode into contact With the electrolyte over an area substantially less than the area of contact of the globule with the part and Without touching the resist or the tungsten carbide part, passing an electric current from the electrode through the electrolyte to the surface of the part exposed through the markings cut in the resist, and continuing the flow of current until the block is marked to the desired depth.

DOUGLASS C. FONDA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 534,895 Legate Feb. 26, 1895 1,376,365 Wertheimer Apr. 26, 1921 1,844,928 Slepian Feb. 9, 1932 2,385,198 Engle Sept. 18, 1945 OTHER REFERENCES Zeitschrift fur Metallkunde, vol. 16 (April 1924), pages 132, 133. 

